Electric wires are provided in vehicles for portions, such as doors that are opened and closed and sliding seats, whereat they are forcefully bent. For example, a plurality of electric wires, which serve as electrical connectors between doors and other automobile body parts, are extended between the doors and the body and pass through bend protection members, called grommets, that are fixed to the hinges by which the doors are installed on the body.
Since grommets and electric wires are bent repeatedly, whenever automobile doors are opened and closed or sliding seats are moved, the ability to predict the durability or the product life of grommets and wires and how well they can withstand the effects produced by bending is important. Conventionally, design, test manufacturing and actual bending tests are repeatedly performed to provide a basis for predicting the durability of grommets and electric wires and how well they will resist the effects produced by bending. On the other hand, since the trend is for the development period for an automobile to be constantly reduced, improvement in prediction accuracy is sought. Thus, as in patent document 1, methods have been proposed whereby test manufacturing can be eliminated and bending durability predicted by performing computer simulations.
Patent Document 1
JP-A-2002-260460
Non-Patent Document 1
“Matrix Infinite Element Method”, B. Nass, Brain Book Publishing Co., Ltd., Aug. 10, 1978, pp. 7-5
Non-Patent Document 2
“Numerical Simulation Using Partial Differential Equation”, Nobuyoshi Tosaka, Tokyo University Publisher, First Edition, Apr. 1, 1991, pp. 119-123
According to the bending durability prediction method in patent document 1, a plurality of electric wires inserted through a grommet are regarded as a wire bundle model, and based on this model, the product life of the wire bundle is predicted. However, since several types and a multiplicity of wires are inserted through a grommet, when the method in patent document 1 is used it is difficult to accurately identify which portion of a wire is damaged first. Further, according to the method in patent document 1, although a set consisting of a plurality of electric wires and a grommet are always employed at a bend, only the product life of the wire bundle is predicted. Therefore, another method is required that can predict the overall product life, including the product lives of the individual electric wires and the grommet. In other words, an improvement is required that can cope with requests for shortening the development period and for improving the prediction accuracy.